S Io Frequency

Figure 7. Comparison of pseudo-Rayleigh noise spectrum with the output spectrum of the GR 1382 generator.

Figure 5. This difference does result in a detectable change in the number of peaks above a given level.

A schematic diagram of how pseudo-Rayleigh noise can be produced from two GR 1 382 Random-Noise Generators 1 is shown in Figure 6. High-conductance germanium diodes, such as 1N455 or 1N695, should be used for low forward voltage drop. A dc amplifier will be needed if it is necessary to reduce the output impedance level or to provide more power.

The effect on the spectrum of this method is shown in Figure 7. This is a comparison of the measured input and output spectra of the system shown in Figure 6. In Figure 7, the spectra are normalized to the same level at low frequencies. This method of approximating Rayleigh noise simply spreads the spectrum a little towards higher frequencies. Similar spreading probably will occur with the true Rayleigh system shown in Figure 3.

This easily assembled system for generating pseudo-Rayleigh noise includes only noise generators, diodes, and resistors. It produces noise having a close approximation to the Rayleigh amplitude distribution.

A brief biography of Dr. Faran appeared in the March/April, 1969 issue of the Experimenter.

1 Faran, J. J., "Random-Noise Generators," General Radio Experimenter, January 1968.

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